The cracked bed of Utah's drought-plagued Lake Powell bakes under the desert sun. The rate of evaporation in deserts can be 20 times higher than the rate of precipitation.

Photograph by Peter Essick

By John G. Mitchell

Republished from the pages of National Geographic magazine

The world's largest freshwater system has shrunk before, but never so quickly. In Traverse City, Michigan, empty chaises at a resort—on what once was lake bottom—reflect how the Great Lakes tourist economy has slipped in sync with falling water levels. And the farther the waters recede, the higher anxiety rises.

It takes a long time to learn how to get along with a lake. A decade isn't half enough. A generation might do. Then, if you have lived that long beside a lake the size of Michigan, you begin to understand that there's something about the fluctuating level of the water that makes no apologies for any inconvenience it may cause. Here is a wide sandy beach; thbenefere, a cottage perched at the lips of a crumbling bluff. Now you see them, now you don't. It's enough to keep a person guessing. The lake couldn't care less.

On the Old Mission Peninsula in Lake Michigan's Grand Traverse Bay, Ted Cline gave up guessing years ago. Since 1957 he and his wife, Jean, have lived here in a home overlooking the bay. From the edge of the lawn, steps go down to a fine sand beach, almost to the water when the level's up. But not long after the Clines moved in, they had to take a walk to wet their feet—the level of Lake Michigan had fallen lower than at any time since surface measurements were first recorded in the 19th century. A shade over 20 years later the lake was up again, higher than it had been in a century, lapping at the foot of the Clines' steps.

Last summer I stood with Cline above the lake and saw how it might have looked back in that earlier record-low time of 1964. For now, after years of drought and simmering annual temperatures, the levels of the Great Lakes had fallen once again, all the way from Duluth, Minnesota, to Kingston, Ontario, at the head of the St. Lawrence River. This is not just a matter of inconvenience to a hundred thousand riparian landowners along U.S. and Canadian shores, though more than a few of them are being put to the expense of extending their docks. It is a matter of concern to the multitudinous cities and farms dependent on lake water, to the boating and fishing segments of the region's multi billion-dollar tourism industry, and to the operators of deep-draft ships that ply these inland ports and waterways to hitch North America's heartland to the markets of the world.

And right here the wide, weedy beaches and rocky shoals of the Old Mission Peninsula said it all: Another couple of years of climatic deprivation and the greatest of these lakes might well bottom out at levels lower than any recorded in historic times.

"Oh, the lake will come back up someday," Cline said. A retired surgeon and World War II leatherneck dive-bomber pilot, he has seen much of the upper Great Lakes from the cockpit of his private plane, flying aerial photography assignments for books and magazines. Now, at the top of the steps above his dehydrated beach, I could only say to Cline, "I hope you're right."

The Great Lakes—Superior, Michigan, Huron, Erie, Ontario—along with the rivers, channels, and lesser lakes feeding or draining them, constitute the largest surface freshwater system on Earth. The system is spread across more than 94,000 square miles (243,460 square kilometers) and drains a much larger watershed that embraces parts of eight states and two Canadian provinces. If only the Earth were flat and the lakes adaptable as buckets, there'd be enough H20 here to flood all the land of the Western Hemisphere under two feet of water.

A complex hydrologic cycle orchestrates the volume of water contained in this system at any one time. And the volume, of course, dictates the levels.

The cycle begins in the clouds. Rain and snow fall across the lakes and the surrounding watershed lands, where runoff replenishes the system's tributaries and aquifers, and they, in turn, replenish the lakes. But that's only half of the cycle. The other half takes some of the water away through evaporation from the surface of the lakes and transpiration from terrestrial plants throughout the watershed. When the inflow from precipitation and runoff is exceeded by the loss of water due to evaporation and transpiration and outflow down the St. Lawrence River, then the levels of the Great Lakes have nowhere to go but down.

Evaporation seems to be winning. By most accounts six of the warmest years on record in this region occurred in the past decade. That not only increased the rate of evaporation in the summertime but also raised it in the winter by depriving the lakes of their normal ice cover. Ice inhibits evaporation. With the exception of Erie, the shallowest of the five, the Great Lakes rarely freeze shore to shore but often ice up in their bays and mid-lake areas. In recent years, however, ice cover did not occur in some places accustomed to freeze or, if it did occur, came in later and went out earlier than usual, which raises the question of global warming.

Lake levels throughout the system are also hugely influenced by the annual snowpack and subsequent snowmelt runoff, especially in the headwater country of Lake Superior. Over three of the past five years, snowpacks around the three upper lakes have yielded runoffs significantly below average. "Springtime has been starting six weeks earlier than normal around the northern lakes," said Roger Gauthier, a senior hydrologist with the U.S. Army Corps of Engineers in Detroit. "The only snow we've seen this year has been lake-effect snowmoisture that evaporates off the lakes and then falls as snow, sometimes outside the basin. That doesn't help their levels any."

Behold the outline of Lake Superior, and you behold the west-facing head of a wolf. At the snout sit the port cities of Duluth, Minnesota, and Superior, Wisconsin (combined population 118,500), which move up to 40 million metric tons of cargo eastward through the Great Lakes every year. Behind the snout our limnetic wolf is getting thirsty.

On the day of my visit two big ships were loading wheat for export to the Mediterranean, a third was taking on Midwest soybeans for a trip to the mouth of the St. Lawrence Seaway, and the holds of a fourth, the Burns Harbor, were inhaling 57,000 gross tons (57,900 metric tons) of iron ore pellets for delivery to the steel mills near Gary, Indiana. Nearly two-thirds of all steel produced in the United States starts as iron ore here on the shores of Lake Superior. At Duluth the tonnage of iron ore is exceeded only by that of coal, which flows to the waiting ships in 123-car trains, a thousand miles from the bituminous seams of Wyoming's Powder River.

Water levels can have a prodigious effect on Great Lakes shipping. According to Davis Helberg, executive director of the Duluth Seaway Port Authority, for every inch of ship's draft clearance lost to low water in the shallower channels, such as the St. Marys River between Lake Superior and Michigan-Huron, a carrier must reduce his cargo by as much as 270 tons (245 metric tons) or risk the danger of running aground. For the owners of these big lake freighters longer than three football fields-the collective cost of low water is estimated at several billion dollars a year.

Albert Tielke, captain of the Burns Harbor, a thousand-footer, told me about a ship that tore a hole in its bottom in Lake Michigan's Grays Reef Passage, east of Beaver Island, a few years ago. "They had to put her in dry dock," he said. "And another ship 'sniffed' the bottom of Calumet Harbor once or twice."

Then Davis Helberg, the port director, put in. "Don't forget the Rock Cut in the St. Marys River," he said. "That's what you have to look out for. There's no forgiveness down there in that cut."

There's not much more forgiveness in the harbors, marinas, and tributary rivers that provide the venue for Great Lakes recreational skippers and sport fishermen. Up the north shore of Superior, up beyond Castle Danger and Beaver Bay, the Baptism and Temperance Rivers looked sluggishly low. I stopped in Grand Marais to check out Wilderness Outfitters, a sales and rental shop catering to the paddling clientele of the tributary Boundary Waters Canoe Area Wilderness. Had the lowered level of Superior affected business in any way? "The drought has," said the outfitter. "Some of our rental canoes are coming back here with a lot more dents than ever before."

Navigation can get tricky for yachtsmen and sailors as well. At the Irish Boat Shop in Harbor Springs, Michigan, the shrinking level of the lake has forced David Irish to dredge his marina's channel three years in a row. "It's a fast way to get rid of your cash," he said.

The Tip of the Mitt Watershed Council is a nonprofit organization dedicated to protecting northern Michigan's water resources. Its offices are located in Petoskey, up near the tip of the mitten some people see when they look at a map of Michigan's Lower Peninsula. After the bad economic news I'd been hearing around the lakes, I wanted to learn a bit about environmental impacts and expected that news would be bad as well. At Tip of the Mitt it wasn't.

"Periodic low water levels are important," Wil Cwikiel was saying. Cwikiel is the council's coastal specialist. "Wetlands and exposed bottomlands are among the most biologically productive ecosystems in the Great Lakes," he said. "We've seen extensive use of these exposed flats by shorebirds and other wildlife. Exposed, the land sprouts new vegetation. And when the levels rise again, there's good habitat for the aquatic creatures. If we're to retain a productive fishery in the lakes, we've got to maintain the food chain fish need to survive."

Cwikiel lamented the tendency of many people to yearn for a static system in which the water levels might be stabilized. "It won't happen," he said. In fact, the most recent study by the International Joint Commission on the Great Lakes concluded that the costs of engineering works to further regulate the system's flows and levels not only would exceed the benefits provided but also would result in serious environmental impacts.

"If only we could begin to think like a Great Lake," Cwikiel said, "and not worry about how far we'll have to walk on the beach to get to the water. Then we'd realize that in all parts of the levels cycle there are beneficial processes."

While lake levels early this year actually rose a bit, many experts, like Cwikiel, still worry about future levels. What if recent drops have not been just part of a natural fluctuation? What if there's truth in what some scientists say about the water levels dropping because of global warming?

"Well," said Cwikiel, "that's the wild card."

I was turning that card over in my mind as I drove north up the lake road toward the ultimate tip of the mitt. Although there is still some uncertainty about the effects of global warming, current studies suggest that under some scenarios the water level of the Great Lakes could be further lowered by three feet or more by the middle of the 21st century. Confronting a number like that, how can anyone think like a Great Lake?

North by Northwest of Petoskey and Harbor Springs a steep bluff shoulders its way down to Lake Michigan under birches and hemlocks and maples, then plays out across a yellow sand beach that is shown on some maps as Sevenmile Point. Once upon a summertime I played there too; learned how to swim there, how to build castles, how to skip stones. I suspect I was a little afraid of Lake Michigan those days, even from the safety of the beach. The lake looked so huge. Couldn't see across it. Bucking the prevailing winds, you'd have a hundred miles of whitecaps and blue water (someone probably said) before you could haul out over there in Wisconsin. Then I learned in school about the other Great Lakes and how, put together, they contain a fifth of the world's fresh water.

Now that ought to be plenty of water to go around. Right? Probably not.

Regardless of what climate change may have in store for the Great Lakes, there will always be some level of consumptive human use water that is withdrawn from the system and not returned to it directly. Current withdrawals for municipal drinking and industrial uses amount to barely a drop in the bucket, for most of the water eventually finds its way back to the system after treatment or in the flow of recharged groundwater. The only significant diversion that does not get back into the system is the 2.4-billion-gallon-a-day (about 9-billion-liter-a-day) draw Chicago extracts from Lake Michigan. For the sanctity of its beaches, Chicago posts its treated wastewater into a sanitary canal, which drains through the Des Plaines River to the Gulfbound Mississippi. This diversion, however, is no great loss to the system because up in Lake Superior it is offset by two positive diversions. These, in effect, pluck water from Ontario's Hudson Bay watershed and transfer it into Lake Superior. On its way south the Ontario water is used to generate hydroelectricity.

Though the United States and Canada have imposed a temporary moratorium on further diversions or bulk exports of water, there's constant fear in this region that some other region with sufficient political muscle—California, for example, or the Southwest—might find a way to tap the lakes. And, in fact, the record is replete with attempts to do just that.

In the 1950s a scheme emerged under the grandiose acronym GRAND, the Great Recycling and Northern Development project. The idea was to isolate James Bay from Hudson Bay with a dike to keep out the salt water and then, by reversing the flow of some Canadian rivers, pipe fresh water into Lake Huron, where transfers to a thirstier region would be possible. The scheme sank under its own grand weight.

In the 1980s someone came up with the bright idea of tapping the Great Lakes to recharge the thirsting Ogallala aquifer under the Great Plains. The U.S. Army Corps of Engineers said "No." Then in 1998 a deal was almost cut that would have permitted a Canadian firm to ship Superior water for bulk sales in Asia. And earlier this year Nestle Waters North America received permission to bottle up to 210 million gallons (about 800 million liters) a year from an aquifer north of Grand Rapids that recharges the Muskegon River, a major Lake Michigan tributary. That one is being challenged in the courts.

Paul Simon, the former Illinois senator, presidential candidate, and author of articles and books about global water shortages, believes it will be only a matter of time before piping bulk exports of water out of the region becomes politically and economically feasible. "Tapping the Great Lakes is going to happen," said Simon, who frowns on the prospect. "If there isn't a big push on desalinization in the West, I'd say it's going to be inevitable!

I thought of Simon's prophecy the afternoon I revisited the wide beach at Sevenmile Point. It was hot. A calm had settled across the water like a tight shroud. No whitecaps, just a flat horizon without a sail, out there at the bottom of the sky near Beaver Island. It occurred to me then that between Simon's grim vision and the wild-card models of global warming, there might not be a whole lot of wiggle room left for learning to live with the natural, cyclical ebb and flow of the Great Lakes.

With that, I found a small, wave-slicked stone and, remembering the barefoot boy at the edge of a hundred miles of whitecaps, skipped it toward Wisconsin.